[compiler-rt] [rtsan][test] Prevent test check from being optimized out in LTO builds (PR #122524)

[Paul Kirth via llvm-commits]

ilovepi wrote:

For context this is required to land #121819, since the copy large lambda test will fail otherwise, due to being completely optimized out when building the Runtimes w/ LTO enabled.

https://github.com/llvm/llvm-project/pull/122524